Industrial truck

ABSTRACT

An industrial truck for handling pallets. The truck includes a drive unit and a load unit. The load unit includes two load-receiving arms that receive the pallet and that are oriented in the direction of motion of the truck, i.e., in a longitudinal direction of the industrial truck. The load-receiving arms, when viewed from the direction of motion of the truck, are provided on different sides of the pallet to be picked up and include a plurality of pallet pick-ups that are spaced apart in the direction of motion of the truck and that are engaged or disengaged with the pallet by a transversal motion with respect to the direction of motion of the truck.

TECHNICAL FIELD

The invention relates, in general, to an industrial truck with a drivepart and a load part for handling packed or empty pallets, in accordancewith the preamble of Claim 1 and, in particular, to an industrial truckfor handling pallets of a certain format, such as those used in thecommissioning sector and in the transport of piece goods.

STATE OF THE ART

Such an industrial truck is known from U.S. Pat. No. 4,101,040. The loadpart has two load arms in the form of fork prongs that are oriented inthe travel direction, i.e. the longitudinal direction of the industrialtruck, and can be raised vertically, with which loads such as pallets orgoods packed on pallets can be handled. The term “handling” includesactivities such as picking up, transporting, and setting down a pallet,goods packed on a pallet, or a stack of pallets. Other examples of suchindustrial trucks are conventional manual forklifts, electric forklifts,wheel-supported stackers, counterweight stackers, or reach mast trucks.In order to pick up a pallet or goods packed on a pallet, the pallet isparticularly provided with suitable recesses for engagement of the forkprongs of the industrial truck, for example of a stacker.

In the transport of piece goods, and in the commissioning sector ofcommercial facilities, the pallets used are predominantly pallets madeof wood, with a certain format, particularly so-called euro-pallets witha length of 1200 mm, a width of 800 mm, a height of 150 mm, and a weightof about 20 to 30 kg. In such facilities, quite a large number of emptypallets that are not needed are often left behind on the floor afterroll-out cycles have been completed, and until now, these had to bestacked, either manually or using one of the aforementioned commerciallyavailable industrial trucks, to form pallet stacks of 15 to 17 pallets,for example (corresponding to the inside height of a transport truck),that could be transported and loaded. Making such a stack by handinvolves a high level of physical effort. For this reason, the emptypallets are usually handled with one of the aforementioned industrialtrucks.

However, the use of conventional industrial trucks for handling emptypallets proves to be extremely inefficient, since the activities thatare involved in this task can only be performed with a high level oftime expenditure, and therefore result in high personnel costs. In orderto stack several empty pallets that are lying around on the floor into apallet stack, for example, using one of the aforementioned industrialtrucks, first the truck is driven towards a first empty pallet and thefork prongs of the industrial truck are placed under the first pallet.Subsequently, the first pallet is raised to a certain height, by meansof a vertical movement of the fork prongs. In this condition, theindustrial truck is driven towards a second pallet, specifically in sucha way that the first pallet is essentially aligned with the secondpallet. Then the first pallet is set down on the second pallet. At thispoint in time, the fork prongs are still engaged with the first pallet.In order to place a third pallet onto the pallet stack that now consistsof the first and the second pallet, or to place this pallet stack onto athird pallet, the industrial truck must therefore first be put intomotion in such a way that the fork moves out of the first pallet.Subsequently, the fork is lowered. Now the second pallet that is locatedon the floor, or the third pallet, can be approached and lifted.Subsequently, the stated steps can be repeated.

Without discussing the matter further, it is evident that stacking apallet stack that consists of 15 to 17 empty pallets, for example,requires a constant back and forth movement of the industrial truck,particularly because of the fork prongs that project in the direction oftravel, i.e. the longitudinal direction, in order to move the fork froma pallet in a higher position into a pallet in a lower position, or viceversa. This is very time-consuming and is accordingly connected withhigh personnel costs. The same holds true for unstacking empty palletsthat have already been stacked together to form a stack, whichfundamentally takes place in the reverse sequence as stacking the emptypallets.

In order to guarantee problem-free handling during pallet storage in ahigh-shelf facility or in automatic pallet packing, the palletsfurthermore are not allowed to demonstrate any damage, such as piecessplintered off, missing wooden parts, etc., since the damaged palletscannot be transported, or can be transported only with restrictions, andmight no longer be suitable for use in a high-shelf facility, becausethey might no longer meet the static requirements. Severely damagedpallets can therefore no longer be used. In order to keep theacquisition costs for new pallets low, a high level of pallet quality istherefore considered to be very important. For this reason, a person whois entrusted with the operation of conventional industrial trucks or, ingeneral, with the handling of empty pallets, requires a certain amountof practice in order not to damage the pallets with the fork of astacker while bringing the fork into place, and in order to accomplishthe task to be performed within a reasonable amount of time.

Furthermore, in order for a pallet stack made up of 15 to 17 emptypallets to possess the necessary stability to prevent it from tipping tothe side, and to allow it to be temporarily stored or loaded onto atransport truck to take up as little space as possible, the pallet onthe top of the pallet stack, in each instance, must be precisely alignedwith the pallet under it, in each instance. This again presupposes acertain level of experience in the operation of the industrial truck.The number of persons who are able to assure safe handling of pallets,using conventional industrial trucks, is therefore limited to speciallytrained personnel.

Other industrial trucks are known from the European Patent ApplicationNo. EP 0 045 553 A1 and the U.S. Pat. No. 3,861,535. EP 0 045 553 A1particularly describes a device for handling several boxes arranged in arow, or several stacks of boxes arranged in a row, using two clampingplates that are arranged opposite one another and can be movedhorizontally towards one another. U.S. Pat. No. 3,861,535 discloses aforklift truck with a forklift mechanism and a carrying device, whichholds pallets or pallet boxes that have been picked up by the forkliftmechanism and raised to a certain height at this certain height.

Presentation of the Invention

Proceeding from an industrial truck as known from U.S. Pat. No.4,101,040, the invention has the task of creating an industrial truckdesigned for simple and efficient handling, particularly of pallets witha certain format, which also allows picking up and transporting loadspacked on a pallet.

This task is accomplished by means of the industrial truck in accordancewith the characteristics of Claim 1.

The industrial truck according to the invention particularlydemonstrates a drive part and a load part, as is the case for aconventional industrial truck. The load part comprises two load arms,oriented in the longitudinal direction of the industrial truck, to holda pallet that can be packed or empty. In conventional industrial trucks,as indicated initially, the load arms are usually structured as forkprongs, which are brought into engagement with recesses provided in thepallet, by means of a forward movement of the industrial truck, forminga positive lock. The load arms are therefore arranged in accordance withthe distance between the recesses, i.e. at a distance that is less thanthe dimension of the pallet to be picked up, in the crosswise directionof the industrial truck. In contrast to this, the load arms of theindustrial truck according to the invention are arranged on differentsides of the pallet to be picked up, in each instance, viewed in thedirection of travel, i.e. the longitudinal direction of the industrialtruck, in other words at a distance that is greater, in the crosswisedirection, than the dimension of the pallet to be picked up, and theyeach have a plurality of pallet holders spaced apart in the longitudinaldirection, which can be aligned towards the pallet, which can be broughtinto or out of engagement with the pallet, in particular with therecesses provided on the pallet, by means of a movement perpendicular tothe longitudinal direction. This movement perpendicular to thelongitudinal direction can take place exclusively by means of a movementof the load arms. Likewise, however, a movement of the pallet holdersprovided on the load arms, or a combined movement of the load arms andthe pallet holders is possible. Furthermore, the movement of the palletholders can consist of a purely horizontal movement and a purelyvertical movement that takes place, in each instance, perpendicular tothe direction of travel, i.e. the longitudinal direction of theindustrial truck. However, the movement of the pallet holders can alsobe achieved by means of a circular movement of the pallet holders, whichcan be broken down into a horizontal component and a vertical componentperpendicular to the longitudinal direction.

Since picking up the pallet, viewed in the direction of travel, i.e. thelongitudinal direction of the industrial truck, takes place by means ofengagement on both sides of the pallet, it is advantageous that theengagement lengths of the pallet holders, which can be structured asfork prongs, as in the case of conventional industrial trucks, can besignificantly reduced. In conventional industrial trucks, the forkprongs must be at least long enough so that they extend beyond thecenter of gravity of the pallet to be picked up, so that the pallet doesnot tip over forwards when it is lifted from the floor. This relativelylong length of the fork prongs increases the risk of damaging the palletwhile the fork prongs pass under it. However, this risk is significantlyreduced by the industrial truck according to the invention.

Since the pallet holders can be brought into and out of engagement withthe pallet by means of a movement perpendicular to the direction oftravel, i.e. the longitudinal direction of the industrial truck, thepallet holders can be implemented in the vertical direction of theindustrial truck, without a constant back and forth movement of thetruck. This contributes to significantly faster and easier handling ofthe pallets, i.e. it allows the formation of a pallet stack orpallet-by-pallet removal of an existing pallet stack in a relativelyshort period of time. Therefore the industrial truck according to theinvention allows efficient handling, particularly of empty pallets.

As explained above, the time expenditure in connection with theactivities involved in the handling of empty pallets can besignificantly reduced by means of the industrial truck according to theinvention. This in turn means a significant savings in personnel andpersonnel costs. Therefore a shipper of piece goods that has to handle adaily turnover of approximately 300 to 400 empty pallets and more canguarantee better working conditions.

Furthermore, since components of conventional industrial trucks can beused to a great extent, the production costs or acquisition costs forthe industrial truck according to the invention are not higher thanthose for a conventional electric pole-arm forklift truck (“ant”).

The industrial truck according to the invention can therefore beimplemented as a stand-alone device or in the form of a specialattachment for a wheel-supported stacker, counterweight stacker, orreach mast truck.

Although the industrial truck according to the invention is specificallydesigned for handling empty pallets of a certain format, particularlyso-called euro-pallets, it can fundamentally also be used fortransporting any desired kind of pallet, a load packed on a pallet, or astack of pallets.

Further developments and embodiments according to the invention are theobject of the dependent claims.

In order to be able to pick up and lift an empty pallet that is lying onthe floor, the load arms have to be adjustable, depending on the formatof the pallet to bepicked up, both with regard to a certain distancefrom the floor and with regard to a certain distance from one another.In order not to limit the use of the industrial truck according to theinvention to a certain pallet format, it is therefore advantageous ifthe load arms that hold the pallet holders are adjustable horizontallyand vertically.

Irregardless, the load arms can be provided on a load carriage that canbe moved vertically, as in the case of a counterweight stacker, awheel-supported stacker, or a reach mast truck, which carriage can bemoved up and down along a reach mast that is assigned to the load partor, as in the case of a forklift truck, an electric manual lift truck,or an electric pole-arm forklift truck, they can form wheel arms of theload part, which are supported on the floor by way of load rollers,where the load part can be raised, relative to the drive part,pneumatically, hydraulically, or mechanically. Furthermore, the loadarms can be adjustable in the crosswise direction of the industrialtruck. These measures make a significant contribution to greatflexibility and therefore to a broad spectrum in the area of applicationof the industrial truck according to the invention.

In order to keep the risk of damage as low as possible when picking upthe pallets, the pallet holders furthermore preferably have arotation-mounted contact roller at their end facing the pallet, whichcontacts the pallet when the pallet holder is engaged with it. Arelative movement between the pallet holders and the pallets thereforetakes place by means of a roll-off movement of the pallet holder on thepallet. As a result, the friction forces that occur during a relativemovement are significantly reduced, on the one hand; on the other hand,the likelihood of damage caused by a thrust impact is reduced, ascompared with sharp fork prongs.

Such damage can be restricted even more if at least the outsidecircumference region of the contact roller is made of an elastic andtherefore impact-absorbing material. Another advantage of this structureof the contact roller, particularly in the case of a heavy pallet stackthat consists of a large number of pallets, is that the contact surfaceof the bottom-most pallet, which rests directly on the contact rollers,is increased relative to the pallet material, because of the resilienceof the elastic material, which means that the contact roller pressesinto the pallet material to a lesser degree.

In order to allow problem-free handling of the pallets, even by a groupof persons with less skill, it is furthermore advantageous if theindustrial truck according to the invention has a feed device that makesit possible to guide and place an empty pallet that is lying on thefloor, for example, between the two load arms with the pallet holders,while the industrial truck is in travel mode, by simply “running over”the pallet to be picked up with the industrial truck, i.e. collectingit. In this regard, it is particularly advantageous if this feed deviceextends beyond the load part and the drive part of the industrial truckaccording to the invention, which means that collecting a pallet that islying on the floor, for example, is not limited to forward travel of theindustrial truck, but rather is also possible during reverse travel.

This feed device preferably comprises guide rails assigned to the loadarms, which are aligned in the longitudinal direction of the industrialtruck, where the distance between them, viewed in the direction oftravel of the industrial truck, increases towards the front and rear ofthe industrial truck. With this feed device, pallets that are lyingaround on the floor can simply be “run over”, i.e. collected. The guiderails, in turn, can have a plurality of guide rollers arranged at adistance from one another in the direction of travel, i.e. thelongitudinal direction of the industrial truck, which minimize thefriction forces that occur between the guide rails of the feed deviceand the pallets when the pallets are run over and collected.

Another simplification in the collection of pallets results if the feeddevice has a locking device, preferably provided on the guide rails,which makes it possible to releasably lock the pallet to be picked up inplace in a predetermined holding position between the two load arms. Inthis case, the industrial truck does not have to be stopped after itruns over a pallet, in order to pick it up, i.e. to take hold of it andlift it. Instead, the pallet to be picked up is pushed along in thetravel direction of the industrial truck for a short distance, until itis removed from the floor, since it is held in place in a predeterminedholding position between the load arms. By means of a correspondingadjustment of the speed of travel of the industrial truck, to a speed atwhich the pallet is picked up, i.e. taken hold of and lifted, by the twoload arms, in this case the distance over which the pallet is pushedwhile it is lying on the floor can be minimized.

If, in addition to the locking device, a pick-up position sensor is alsoprovided, which detects whether or not the pallet has taken thepredetermined holding position, and indicates this by giving off acorresponding electrical signal, the operator of the industrial truckcan effect pick-up of the pallet as a function of the electrical signal,by means of activating the load arms and/or the control device that iscoupled with the holding position sensor. Of course, it is advantageous,in this regard, if the control device automatically activates the loadarms and/or the pallet holders as a function of the electrical signal,since in this case the operator of the industrial truck only has to payattention to running over the pallets to be collected with the shortestpossible path. Pallet-by-pallet distribution of the pallets alreadystacked in a stack on the floor is also particularly simple when usingthe control device.

A preferred embodiment of the industrial truck according to theinvention consists of the fact that the load arms each comprise arotation-mounted roller, the axis of rotation of which is aligned in thelongitudinal direction, i.e. are structured in roller form, where thepallet holders preferably extend tangentially over the outsidecircumference of the roller, in each instance. By means of asynchronous, opposite rotational movement of the two rollers in adirection of rotation that is determined, in each instance, the palletholders can be brought into engagement with the pallet to be picked up,in such a way that the pallet which is being picked up is already liftedto a specific height simply by the further rotational movement of therollers. A further rotational movement of the load arms would have theresult that the pallet holder goes out of engagement with the liftedpallet, which would cause it to fall to the floor.

Once the pallet holders have been brought into engagement with thepallet, however, lifting the pallet could also be brought about by avertical movement of the load arms, i.e. lifting of the pallet could beachieved by means of a rotational movement of the load arms incombination with a vertical movement. Of course, the rollers must bepositioned in such a way, relative to the floor and the pallet to bepicked up, i.e. they must be adjusted by means of a horizontal andvertical adjustment of the load arms and/or the pallet holdersperpendicular to the direction of travel, i.e. the longitudinaldirection, so that when a rotational movement of the rollers occurs, thepallet holders do not touch the floor, on the one hand, and they can bebrought into and out of engagement with the pallet to be picked up, onthe other hand. In this connection, the diameter of the circle describedby the ends of the pallet holders, in each instance, during a rotationalmovement of the rollers, must also be coordinated with the pallet formatin each instance.

With regard to the most efficient handling of empty pallets that ispossible, particularly with regard to unstacking an existing palletstack, it is advantageous if the rollers each have a plurality of palletholders spaced uniformly apart in the circumference direction of therollers. In this case, but of course only if the rollers and/or thepallet holders are appropriately coordinated with the distance from thefloor and the pallet format of the pallets to be picked up, a palletstack can be formed from any desired number of pallets, or an existingpallet stack can be unstacked, within a relatively short period of time,by means of a synchronous, opposite rotational movement of the rollersin the direction of rotation determined in each instance.

Forming a pallet stack by means of the industrial truck according to theinvention can be implemented, for example, in that individual emptypallets that are lying around on the floor are “run over” by theindustrial truck according to the invention, in at such a way that theyare placed between the two load arms by the feed device described above.After the predetermined holding position between the two load arms ofthe industrial truck has been reached, in which the pallet that has beencollected is held in place by the locking device, specifically even iftravel continues, which position is detected by the holding positionsensor, the rollers are activated, preferably automatically, to put theminto a suitable rotational movement. In this connection, the palletholders engage into the collected pallet and take the pallet with them,in an upward direction, during the course of the further rotationalmovement of the rollers. As soon as this pallet has reached a heightthat is sufficient to place another pallet under the pallet that hasbeen lifted, the rotational movement of the roller is stopped.Immediately after this procedure, the next pallet can be run over andcollected. Only after it has been detected, once again, that thecollected pallet has been placed in the predetermined holding positionbetween the two load arms, the load arms are put into a rotationalmovement in the opposite direction, causing the first pallet to be setdown on the collected pallet underneath it. Unhindered movement of therollers in the opposite direction of rotation is only possible, however,once the pallet holders have come out of engagement with the pallet inthe higher position, viewed in the crosswise direction. For thispurpose, the pallet holders must be able to perform a horizontalmovement perpendicular to the longitudinal direction, by means of whichthey are moved away from the pallet. This can be achieved in that theyare coupled with the roller, in each instance, in wing like manner, insuch a way that they assume the aforementioned tangential position underthe effect of a bias force, and can be pivoted into a circumferenceposition, counter to the bias force, in which they are essentiallyaligned in the circumference direction of the roller. The horizontalmovement of the pallet holders could also be achieved, in general,however, if the pallet holders are rigidly attached to the load arms andthe load arms are adjusted horizontally, perpendicular to thelongitudinal direction.

The wing-like coupling of the pallet holders with the load arms is alsoparticularly advantageous for unstacking empty pallets that have alreadybeen formed into a stack. For unstacking, the industrial truck accordingto the invention first picks up a stack of empty pallets, in that itactivates the rollers in such a way that the pallet holders are broughtinto engagement with the bottom-most pallet of the pallet stack, bymeans of a rotational movement of the rollers in a certain direction ofrotation, in each instance, and the pallet stack is lifted. Aftertransport of the pallet stack to a desired location, the rollers areactivated in such a way that they perform a rotational movement in theopposite direction of rotation, causing the entire pallet stack to firstbe set down on the floor. The rotational movement of the rollers is thencontinued until the pallet holders or, in the case of several palletholders distributed over the circumference of the rollers, the nextpallet holders, engage with the pallet lying in the second row, viewedfrom the floor up. Since the pallet holders are coupled with the roller,as described above, they can pivot towards the roller and glide alongthe pallet stack under the pallet that is lying in the second row, ifthey hit against the pallet stack from the top, in each instance, duringthis continued rotational movement of the rollers. If the pallet holdersare rigidly attached to the rollers, the load arms and/or the palletholders must, of course, perform a horizontal movement perpendicular tothe longitudinal direction. Now the rollers are activated again, in sucha way that they perform a rotational movement in the first direction ofrotation, in order to lift the pallet stack, starting from the secondpallet, viewed from the floor up, thereby releasing the bottom-mostpallet and making it possible to leave it behind.

Forming a pallet stack, or unstacking individual pallets from anexisting pallet stack, could also be implemented in a different way,however. For example, the load arms could have a plurality of transportdevices spaced apart in the longitudinal direction and alignedvertically, in each instance, with a transport means, such as a conveyorbelt or a conveyor chain, on which the pallet holders are attached, ineach instance. In this case, the transport means, in each instance, canbe controlled to be synchronous in opposite directions. The palletholders are aligned towards the pallet, preferably normally, on thetransport means in each instance. Here again, it would be advantageousif the transport means each have a plurality of pallet holders, spaceduniformly apart in the direction of movement of the transport means, ineach instance, and/or the pallet holders are coupled with the transportmeans, in each instance, in wing-like manner, as in the case of theroller, in such a manner that they assume the normal position under theeffect of a bias force, and can be pivoted into a parallel positioncounter to the bias force, in which position they are essentiallyaligned parallel to the transport means.

The industrial truck according to the invention is particularly designedfor handling empty pallets of a specific format, for example so-calledeuro-pallets. Therefore the industrial truck preferably has a holdingdevice adapted to the format of the pallets, which is placed above theload arms and makes guided pick-up of empty pallets in the verticaldirection of the industrial truck possible. On the one hand, thiseliminates the risk of tipping of a pallet stack formed of severalpallets. On the other hand, precise alignment of the pallets above oneanother is made possible.

In an advantageous further development, the holding device comprises alocking device, for example one or more spring-biased pivot hooks, whichallow(s) releasable locking of the empty pallet(s) held in the guidebasket at a certain height. This further development facilitates boththe formation and the unstacking of a pallet stack, since it creates thepossibility of holding the pallet stack in place, starting from anydesired pallet, for example the second pallet from the bottom, by way ofthe locking device, while the bottom-most pallet can be set down on thefloor, by means of the engagement of the pallet holders and appropriatecontrol of the load arms. Subsequently, the pallet stack being held inplace by the locking device can be taken over by the load arms again andthe procedure described above can be initiated once again.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic side view of a preferred embodiment of theindustrial truck according to the invention.

FIG. 2 shows a schematic cross-sectional view along line II—II in FIG.1.

FIG. 3 shows a schematic cross-sectional view along line III—III in FIG.2.

FIG. 4 shows a schematic top view of the preferred embodiment of theindustrial truck according to the invention, where a holding basket thatis arranged above the load arms is left out for the sake of simplicity.

FIG. 5 shows a schematic perspective view of the preferred embodiment ofthe industrial truck according to the invention, where a holding basketthat is arranged above the load arms is left out for the sake ofsimplicity.

FIGS. 6a to 6 d illustrate the method of operation of the industrialtruck according to the invention in the formation of a pallet stack.

FIGS. 7a to 7 d illustrate the method of operation of the industrialtruck according to the invention in the unstacking of an existing palletstack.

PREFERRED EMBODIMENT OF THE INVENTION

The preferred embodiment of the industrial truck 1 according to theinvention will be described below, making reference to FIGS. 1 to 6.

As is shown in FIG. 1, for example, the industrial truck 1 according tothe invention, which is similar to an electric forklift truck, comprisesa drive part 2 and a load part 3. In the region of the drive part 2, theindustrial truck 1 stands on the floor, with a steerable drive wheel 21and a pivot roller (not shown).

A battery compartment (not shown) to provide power to an electric motor(not shown) that drives the truck, as well as an electric roller driveengine (not shown), are housed in the drive part 2. Furthermore, thedrive part 2 comprises a control console 22 with a pivoting operatinglevel 23 for forward and reverse travel, a steering wheel 24, an on/offswitch 25, a battery level indicator 26, as well as several switches andindicator lights 27 to indicate the functions being performed by theindustrial truck 1, the control and drive modi with regard to traveldrive, roller drive, and the like. On the side of the drive part 2 thatfaces away from the load part 3, there is a platform 29, on which theperson operating the industrial truck sits or stands, preferablyperpendicular to the direction of travel, i.e. the longitudinaldirection L of the industrial truck. Finally, a foot-activated safetyswitch 28 is provided on the platform 29, which does not allow operationof the industrial truck until it is activated by the operator.

The load part 3 comprises two wheel arms 32 and 33 that extend in thelongitudinal direction, which support the load part 3 of the industrialtruck 1 on the floor B with load rollers 34 and 35, respectively. Asindicated in FIG. 4, the wheel arms 32 and 33, viewed in the crosswisedirection Q of the industrial truck 1, are arranged at a distance D fromone another, which is so great that a pallet 38 to be picked up, forexample a so-called “euro-pallet” with a length of 1200 mm, a width of800 mm, and a height of 150 mm, can be arranged between the wheel arms32 and 33, i.e. between the load arms 36 and 37 described below.

The load part 3 furthermore has the two load arms 36 and 37, which aresupported on the drive part 2 or on the wheel arms 32 and 33,respectively, as is evident from FIG. 3, for example. The load arms 36and 37 have the function of holding, that is grasping and in lifting orsetting down a pallet 38 that is arranged between them, which, by theway, can be packed or empty. In the preferred embodiment, the load arms36 and 37 are structured as rollers, in each instance, which are mountedto rotate around an axis of rotation 39 and 40, respectively, of thecorresponding wheel arm 32 and 33, respectively, and the drive part 2,as is evident from FIGS. 2 and 4, for example. It is true that in thepreferred embodiment, the axes of rotation 39 and 40 of the two rollers36 and 37 are arranged to be stationary horizontally and vertically, butthey can be adjusted, for example before the first start-up of theindustrial truck, or within the framework of maintenance work.

Two groups 36 a and 36 b, and 37 a and 37 b, respectively, of wing-likecoupled pallet holders 42 are provided on the rollers 36 and 37,respectively. The two pallet holder groups 36 a and 36 b, and 37 a and37 b, respectively, are arranged spaced apart in the longitudinaldirection, where the distance is adapted to the distance between therecesses (not shown) in pallet 38 that are provided to hold it.

As is particularly evident from FIGS. 2, 5, and 6 a, each pallet holdergroup 36 a and 36 b, and 37 a and 37 b, respectively, viewed in thecircumference direction of the roller 32 or 33, respectively, eachcomprises three pallet holders 42 spaced uniformly apart, which arecoupled with the corresponding roller 32 or 33, respectively, inwing-like manner, by means of a spring-biased hinge 44, specifically insuch a manner that the pallet holders 42 tend to assume a tangentialposition, in which they extend essentially tangentially over the outsidecircumference of the corresponding roller 32 or 33. However, the palletholders can be pivoted into a circumference position, counter to thebias force, in which they are aligned essentially in the circumferencedirection, as is evident, for example, from FIG. 6d.

The pallet holders 42 each have a contact roller 45 mounted at the endthat enters into contact with the pallet 38, which rolls along thepallet 38 when the pallet holder 42 engages with it. In the preferredembodiment, the contact rollers 45 are each made from an elastic andtherefore impact-absorbing material.

During a synchronous, opposite rotation of the rollers 36 and 37, thecontact rollers 45 of the pallet holders 42 move in a circular path 43,in each instance. The distance between the axes of rotation 39 and 40 ofthe two rollers 36 and 37, respectively, as well as the diameter of thecircular paths 43 are particularly set or predetermined in such a waythat the pallet holders 42 engage in corresponding recesses of thepallet 38 that is arranged between the rollers 36 and 37, during theircircular movement, and take the pallet 38 with them during furthercircular movement, and lift it to a certain height H, as is evident fromFIGS. 6a to 6 d. By means of a synchronous, opposite rotational movementof the two rollers 36 and 37, the pallet holders 42 are therefore in aposition to pick up the pallet 38 and to lift it to a certain heightsimply by means of a further rotational movement. A further rotationalmovement of the load arms would then have the result that the palletholders go out of engagement with the lifted pallet, which would causethe latter to fall to the floor. Therefore the rotational movement ofthe rollers 36 and 37 is stopped as soon as the pallet 38 has reachedthe predetermined height (corresponding to the pallet height including asafety gap of approximately 2 cm).

The wheel arms 32 and 33 of the industrial truck 1 are furthermorestructured in such a way, in particular, that they allow an arrangementof the rollers 36 and 37, including the pallet holders 42, thatunhindered rotational movement of the rollers 36 and 37, on the onehand, and unhindered circular movement of the contact rollers 45 of thepallet holders 42, on the other hand, is possible. For this purpose,recesses 60 are provided on the wheel arms 32 and 33, which can be seenin FIGS. 2 and 5, for example. Before start-up of the industrial truck,or within the framework of maintenance work, the rollers 36 and 37 areadjusted in such a way that the pallet holders 42 do not touch eitherthe floor B or the wheel arms 32 and 33, during a rotational movement ofthe rollers 36 and 37 on the one hand, and can be brought into and outof engagement with the pallet 38 to be picked up, with a positive and/ora non-positive lock, on the other hand. In the preferred embodiment, theroller radius is approximately 18 cm, the radius of the circular path 43of the contact rollers 45 of the pallet holders 42 is approximately 42cm, and the floor clearance is approximately 2 cm.

The load part 3 of the industrial truck according to the inventionfurthermore comprises a feed device in the form of a guide channel 49that extends over the load part 3 and the drive part 2 in thelongitudinal direction, which is delimited in the lateral direction bytwo guide rails 50 and 51, each of which is assigned to one of the twowheel arms 32 and 33. The guide rails 50 and 51 guide an empty palletthat is lying on the floor, while it is “run over” or collected by theindustrial truck, between the two rollers 36 and 37, so that these canpick up the pallet 38, as soon as the pallet 38 is located in aso-called holding position AP, viewed in the direction of travel, i.e.longitudinal direction L. Since the guide channel 49, including theguide rails 50 and 51, extends beyond the load part 3 and the drive part2 of the industrial truck 1 according to the invention, a pallet 38lying on the floor can be collected both during forward travel andduring reverse travel of the industrial truck 1.

The guide rails 50 and 51 each have a plurality of guide rollers 52spaced apart in the direction of travel, i.e. the longitudinal directionof the industrial truck 1, which are arranged to rotate around an axisof rotation that is aligned vertically. These guide rollers 52 have thefunction of minimizing the friction forces that occur when a pallet 38that is lying on the floor is run over and collected, between the guiderails 50 and 51 of the feed device and the pallet 38.

In order to position the collected pallet 38 in the holding position APindicated above, which is evident from FIG. 4, locking bolts 53 arefurthermore provided in the guide channel 49, i.e. on the guide rails 50and 51, which can be moved out horizontally, perpendicular to thedirection of travel, i.e. the longitudinal direction L. The lockingbolts 53 allow releasable locking of the pallet 38 to be picked up inthe holding position AP between the two rollers 36 and 37. Theindustrial truck 1 therefore does not have to be stopped after a pallet38 has been run over and collected, since the collected pallet 38 isheld in place in the predetermined holding position AP, in which it canbe held by the pallet holders 42. Instead, the pallet to be picked up ispushed along for a short distance in the direction of travel of theindustrial truck 1, after it has assumed the predetermined holdingposition AP and before it is removed from the floor B. By suitablyadjusting the speed of travel of the industrial truck to the speed atwhich the pallet 38 is picked up, in this case the distance over whichthe pallet 38 is pushed while lying on the floor can be minimized.

In addition to the locking bolts, holding position sensors 54, forexample in the form of end position switches or sensors, are furthermoreprovided, which detect whether or not the pallet 38 has assumed thepredetermined holding position AP and, if applicable, indicate this byissuing a corresponding electrical signal. As a function of theelectrical signal, the operator of the industrial truck 1 can thenrecognize that the pallet 38 is in the holding position AP and can bepicked up.

The drive part 2 of the industrial truck 1 furthermore comprises acontrol device (not shown), by means of which the rollers 36 and 37 canbe activated. This control device is coupled to the holding positionsensors 54 in this embodiment, and does not allow the pallet 38 to bepicked up by means of the rollers 36 and 37 until after the electricalsignal that indicates that the pallet 38 is in the holding position APhas been issued. The operator can select whether he/she will triggeractivation of the rollers 36 and 37 himself/herself, or whetheractivation of the rollers 36 and 37 will take place automatically, as afunction of the electrical signal of the holding position sensors.

In the region of the wheel arms 32 and 33, draw hooks 55 that can bemoved out in the direction of travel, i.e. the longitudinal direction L,are furthermore provided, which serve to pull a pallet that is restingon its side against a wall, and actually cannot be collected by means ofthe industrial truck according to the invention, away from the wall, sothat it becomes accessible for the industrial truck 1 according to theinvention. In the retracted state, these draw hooks do not project, sothat furthermore, a stack of pallets can also be pushed along ahead ofthe industrial truck, using the industrial truck.

Finally, there is a holding basket 60 above the load arms 36 and 37,which has the function of holding the collected and picked-up pallets,guided in the vertical direction, on the one hand, in order to preventthe stack of pallets that has been formed from the pallets that havebeen picked up from tipping over. On the other hand, the holding basket60 also has the function of aligning the pallets that were picked up toform the pallet stack, one after the other, in such a way that a palletstack with outside dimensions that lie within a certain tolerance rangeis formed. Furthermore, an adjustable end switch is attached to theholding basket 60, which indicates that a certain height, and thereforea certain number of stacked pallets, has been reached.

Making reference to FIGS. 6a to 6 d, the operation and the method offunctioning of the industrial truck according to the invention will beexplained below. For this purpose, the formation of a pallet stackconsisting of several pallets will be described.

The formation of a pallet stack using the industrial truck according tothe invention can be implemented in that first, a single pallet 38 thatis lying around on the floor B is run over, i.e. collected, where thecollected pallet 38 is placed between the two wheel arms 32 and 33 and,in a defined position, between the two rollers 36 and 37, by means ofthe guide channel. When the holding position AP has been reached, thecollected pallets are held in the holding position AP by means of thelocking bolts 53, specifically even if the truck continues to move. Theholding position AP of the pallets 38 is detected by the holdingposition sensor 54, whereupon the latter issues a corresponding signal.

As a function of the electrical signal of the holding position sensor,the rollers 36 and 37 are finally activated, either manually by theoperator or automatically by the control device, causing the rollers 36and 37 to be put into rotational motion in the direction of rotationindicated in FIG. 6a, in each instance, whereupon the pallet holders 42each engage in the pallet 38.

Over the course of the continued rotational movement, the pallet holders42 take the pallet 38 along with them in an upward direction, as isillustrated in FIG. 6b.

As soon as the pallet 38 has been lifted so high that sufficient roomfor another pallet 38′ is available under the raised pallet 38, therotational movement of the rollers 36 and 37 is stopped, causing thepallet 38 to be held at the defined height H, for the time being. Thisis shown in FIG. 6c.

In this condition, the next pallet 38′ can be run over and collected.After it has been detected again that the collected pallet 38′ hasassumed the holding position AP, the rollers 36 and 37 are again putinto rotational motion, but in the opposite direction of rotation, as isevident from FIG. 6d, causing the pallet holders 42 to move downward andto set the first pallet 38 down on the pallet 38′.

If the rotational movement of the rollers 36 and 37 continues downward,the pallet holders 42′ bump up against a bottom base board of the firstpallet 38 from the top, and pivot into the circumference position inwhich the pallet holders 42′ are aligned essentially in thecircumference direction of the roller 36 or 37, respectively, counter tothe spring bias force, because they are coupled to the roller 36 or 37,respectively, in wing-like manner, as is evident from FIG. 6d. In thisembodiment, the pallet holders 42 therefore pivot towards the roller 36or 37, respectively, in each instance, in order to be able to glide fromthe pallet 38 in the higher position into the pallet 38′ in the lowerposition. Because of the contact roller, the pallet holders 42′ rollalong the two pallets 38 and 38′ as this happens. As mentioned above,the pivoting movement that is required for this purpose is made possibleby the wing-like coupling of the pallet holders 42 to the rollers 36 and37, in each instance.

After engagement of the pallet holders 42 in the pallet 38′, thedirection of rotation of the rollers is reversed again, causing thepallet holders 42 to lift the pallet stack, which in the meantimeconsists of the pallets 38 and 38′, as shown in FIG. 6a.

The steps described above are now repeated as often as necessary, untilthe pallet stack has reached a certain height, which is detected by theend switch provided on the holding basket. Then automatic or manualactivation of the rollers is terminated. Using the industrial truckaccording to the invention, the pallet stack can now be transported to adesired location, and be set down at this location by pushing a button.

The formation of a pallet stack, i.e. carrying out the steps describedabove, aside from steering the industrial truck, can be carried outeither automatically or manually, i.e. by activation of various functionswitches by the operator of the industrial truck. Collection and pick-upof the pallets can take place in the forward or reverse direction oftravel, because the guide channel extends through the load part and thedrive part. Therefore, in the preferred embodiment, locking bolts andholding position sensors are provided for this purpose, both ahead ofand behind the holding position that is predetermined by the arrangementof the pallet holders, viewed in the direction of travel, i.e. thelongitudinal direction of the industrial truck. However, picking uppallets during forward travel of the industrial truck only makes senseup to eye level, since after that, the pallet stack blocks theoperator's view.

Making reference to FIGS. 7a to 7 d, unstacking of an existing palletstack will now be explained, which fundamentally takes place in thereverse order as formation of a pallet stack.

First, the industrial truck according to the invention picks up anexisting pallet stack of empty pallets 38, 38′, 38″, etc., by taking thepallet stack between the wheel arms and the rollers, and, by means ofappropriate activation of the two rollers, lifts the pallet stack tosuch a height, via the bottom-most pallet 38, that transport of thepallet stack is possible without floor contact, as is evident from FIG.72.

In this state, the pallet stack is transported to the desired location,at which the bottom-most pallet 38 is to be set down, with the palletstack being held at the previously assumed height during transport. Thisis illustrated in FIG. 7b.

At the desired location, a rotational movement of the two rollersdownward takes place by means of manual activation of the two rollers bythe operator, as shown in FIG. 7c, causing the pallet stack to be setdown on the floor B and the pallet holders 42, which until then havebeen engaged with the bottom-most pallet 38, to slide out of thecorresponding recesses. This rotational movement is continued until thenext pallet holders 42′, viewed in the circumference direction anddirection of rotation of the rollers, in each instance, engage in thecorresponding recesses of the pallet 38′ that is second in line, afterhaving rolled along the pallet 38″ that is third in line, performing apivoting movement towards the circumference position, in each instance,as is evident from FIG. 7c.

Subsequently, the rollers are put into rotational motion in the oppositedirection of rotation, as is shown in FIG. 7d, causing the palletholders 42′ to now lift the pallet stack, starting from the secondpallet 38′, specifically so far until the bottom-most pallet 38 isreleased.

Subsequently, the industrial truck, with the pallet stack that has beenreduced by the bottom-most pallet, can be moved to a different location,in order to repeat the steps indicated above. This can be continueduntil the pallet stack has been completely unstacked.

In the following, possible variations of the preferred embodiment andadditional embodiments of the industrial truck according to theinvention will be explained.

In the embodiment described above, picking up the pallets is done inthat the pallet holders move in a circular path, in each instance, bymeans of a rotation of the rollers. Lifting of the pallets thereforetakes place by means of a horizontal movement component and a verticalmovement component of the pallet holders. Once the pallet holders havebeen brought into engagement with the pallet, however, it would also bepossible to lift the pallet in that the rollers are raised vertically,instead of a further rotational movement of the rollers. Likewise,lifting of the pallet could be achieved by means of a combination of therotational and vertical movement of the rollers. Movement of the palletholders perpendicular to the longitudinal direction could take place bymeans of an exclusive movement of the load arms. However, a movement ofthe pallet holders provided on the load arms, or a combined movement ofthe load arms and the pallet holders is also possible.

In the preferred embodiment, the pallet holders are each coupled withthe roller, in each instance, in wing-like manner. However, this is notabsolutely necessary. The pallet holders can also be rigidly attached tothe roller, in each instance, where in this case the pivoting movementof the pallet holders towards the roller, in each instance, which isnecessary in the preferred embodiment, can be circumvented in that therollers, in each instance, are moved away from the pallet, horizontally,perpendicular to the longitudinal direction of the industrial truck.

Instead of the load arms that are structured as rollers, in accordancewith the preferred embodiment, the load arms can comprise a plurality oftransport devices that are aligned vertically and spaced apart in thelongitudinal direction, with a transport means, such as a conveyor beltor a conveyor chain. In this case, the pallet holders, in each instance,would be provided on the transport means, in each instance. Thetransport means could be driven synchronously, in opposite directions.As in the preferred embodiment, the transport means could have aplurality of pallet holders spaced uniformly apart in the runningdirection. Likewise, pallet holders could be coupled with the transportmeans, in each instance, in wing-like manner, by means of aspring-biased hinge, in such a way that they assume a normal positionunder the effect of the spring bias, in which they are normally alignedwith the transport means, in each instance, and can be pivoted into aparallel position, counter to the bias force, in which they are alignedessentially parallel to the transport means.

In another variation of the preferred embodiment, the lead arms could beprovided on a vertically movable load carriage, which can be moved upand down along a lift mast assigned to the load part, as in the case ofa counterweight stacker, a wheel-supported stacker, or a reach masttruck, where the load arms in turn can be adjustable horizontally,perpendicular to the direction of travel, i.e. the longitudinaldirection of the industrial truck. The pallet holders can therefore alsobe structured as prong elements aligned towards the pallet to be pickedup, which can be brought into engagement with the corresponding recessesof the pallet to be picked up, by means of horizontal and verticalmovements, perpendicular to the direction of travel, i.e. thelongitudinal direction of the industrial truck, in each instance.

If the load arms are carried by a vertically movable load carriage, itis possible, in contrast to the preferred embodiment, to unstack anexisting pallet stack not pallet-by-pallet but also in batches.Furthermore, it would also be possible, in this case, to lift a palletor a pallet stack onto a transport truck or a ramp, or down from atransport truck or a ramp.

Furthermore, it would be possible to have the load arms and/or thepallet holders perform an appropriate kinematic movement, for example inthe form of cams and cam followers, as a function of the pallet or thepalleted load to be picked up in each instance, as well as taking intoconsideration the prevailing ambient conditions of the pallet holders,in each instance, including the available space.

The wheel arms could circumvent the load arms laterally, in eachinstance, viewed in the crosswise direction, or could bridge them inyoke-like manner, viewed in the vertical direction.

In an advantageous further development, the holding basket comprises alocking device, for example one or more spring-biased pivot hooks, whichallow(s) releasable locking of the empty pallet(s) held in the holdingbasket, at a certain height. This further development facilitates boththe formation and the unstacking of a pallet stack, since it creates thepossibility of holding the pallet stack in place, starting from adesired pallet, for example the second pallet from the bottom, using thelocking device, while the bottom-most pallet can be put down on thefloor by way of engagement of the pallet holders and the correspondingactivation of the load arms. Subsequently, the pallet stack being heldin place by the locking device can be taken over by the load arms again,and the procedure described above can be initiated again.

The industrial truck according to the invention can be implemented as astand-alone device or in the form of a special attachment device for awheel-supported stacker, a counterweight stacker, or a reach mast truck.

Although the industrial truck according to the invention is specificallydesigned for handling empty pallets of a certain format, particularlyso-called euro-pallets, it can fundamentally also be used for transportof a pallet, a palleted load, or a pallet stack.

Commercial Usefulness

The industrial truck according to the invention is particularly wellsuited for handling empty pallets, for example in the commissioningsector and the transport of piece goods. Use of the stacker ant appearspractical starting from a certain daily number of empty pallets that canno longer reasonably be handled manually. The stacker ant is suitable asa means of transport of packed pallets. Significant advantages inconnection with this activity occur in the transport of special pallets.

What is claimed is:
 1. An industrial truck comprising: a drive partconfigured to drive the industrial truck; and a load part configured tocollect and stack pallets to a stack of pallets and to remove a palletfrom the stack of pallets, the load part comprising two load armsextending in a first direction of travel of the industrial truck, wherefunctions in connection with handling of a pallet are exclusivelyperformed by the load arms, wherein the load arms, viewed in the firstdirection are provided on opposite sides of the pallet to be picked upand have each a plurality of pallet holders spaced apart in the firstdirection, which are configured to rotate one of clockwise andcounter-clockwise to grip and capture a pallet perpendicular to thefirst direction and to rotate in the other one of counter-clockwise andclockwise to release the captured pallet.
 2. The industrial truckaccording to claim 1, wherein the pallet holders are configured to bebrought into engagement with the pallet to form a positive lock.
 3. Theindustrial truck according to claim 1, wherein the load arms areconfigured to be horizontally and vertically adjustable perpendicular toa direction of travel of the industrial truck.
 4. The industrial truckaccording to claim 1, wherein the load part comprises a verticallyadjustable load carriage configured to carry the load arms.
 5. Theindustrial truck according to claim 1, wherein the pallet holderscomprise a rotation-mounted contact roller configured to roll on thepallet during an engagement therewith.
 6. The industrial truck accordingto claim 5, wherein outer surface of the contact roller comprises anelastic material.
 7. The industrial truck according to claim 1, furthercomprising: a feed device configured to guide the pallet to a positionbetween the load arms.
 8. The industrial truck according to claim 7,wherein the feed device comprises a guide channel that extends beyondthe load part and the drive part of the industrial truck, the guidechannel configured to be adjusted to a format of the pallet and tocollect the pallet during at least one of a forward or a reverse travelof the industrial truck.
 9. The industrial truck according to claim 8,wherein the guide channel is delimited by guide rails configured to bedisposed at a side of the pallet, a distance between the guide railsbeing a maximum at one of a front and a rear of the industrial truck.10. The industrial truck according to claim 9, wherein the plurality ofpallet holders comprises a plurality of guide rollers, the plurality ofguide rollers disposed on the guide rails and spaced apart in the firstdirection.
 11. The industrial truck according to claim 7, wherein thefeed device comprises a locking device configured to releasably lock thepallet in a predetermined holding position.
 12. The industrial truckaccording to claim 11, further comprising: a holding position sensorconfigured to detect whether the pallet is locked in the predeterminedholding position and to output a corresponding electrical signal. 13.The industrial truck according to claim 12, further comprising: controldevice coupled with the holding position sensor, the control deviceconfigured to activate at least one of the load arms and the palletholders in response to the electrical signal to add the pallet to thestack of pallets.
 14. The industrial truck according to claim 13,wherein the control device is configured to activate the at least one ofthe load arms and the pallet holders in response to the electricalsignal to add the pallet to the stack of pallets.
 15. The industrialtruck according to claim 1, wherein the load arms comprise arotation-mounted roller to which the pallet holders are attached. 16.The industrial truck according to claim 15, wherein the plurality ofpallet holders is disposed on the rollers and spaced uniformly apart ina circumference direction.
 17. The industrial truck according to claim15, wherein at least one of the pallet holders is coupled with theroller in a wing-like manner such the pallet holder is configured toextend tangentially over an outside circumference of the roller undereffect of a bias force, and is configured to be pivoted into a positioncounter to the bias force.
 18. The industrial truck according to claim1, further comprising: a holding device disposed above the load arms andconfigured to hold the stack of pallets stacked in a vertical direction.19. The industrial truck according to claim 18, further comprising: alocking device configured to release locking of the pallet held in theholding device.